On 9/22/26 11:10 AM, Leo Li wrote:
>
>
> On 2026-09-22 14:04, Matthew Schwartz wrote:
>> On 9/22/26 10:50 AM, Leo Li wrote:
>>>
>>>
>>> On 2026-09-21 15:47, Matthew Schwartz wrote:
>>>> Hi George,
>>>>
>>>> After updating to Linux 7.2.x, I noticed gamescope's frame limiter falling
>>>> below the requested rate. The reproducer was a Navi 33 driving 4K120
>>>> through a DP-HDMI PCON, with VRR disabled. A 40fps limit was producing
>>>> roughly 37fps.
>>>>
>>>> Gamescope was pacing against the fixed 120Hz refresh interval, but we
>>>> observed frame intervals stretching to around 9.34ms instead of 8.33ms.
>>>> The OTG vtotal also increased from 2249 to 2521. This was enough to
>>>> disrupt the limiter's pacing despite userspace leaving VRR_ENABLED=0.
>>>
>>> Hi Matt,
>>>
>>> I wonder if this has to do with re-introducing 2-frame vblank off for NV3+
>>> DGPUs, which made it into 7.2:
>>>
>>> fba211b078d6 ("Revert "drm/amd/display: Restore 5s vbl offdelay for NV3x+
>>> DGPUs"")
>>>
>>> Since gamescope is only updating every 3rd frame, it's possible vblanks were
>>> turned off during those two frames, signaling driver to enable idle
>>> optimizations.
>>>
>>> To test this idea, does bumping this line to something like 5 frames
>>> ((u64)50 *) help?
>>> https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c#L3377
>>
>> Tested this by reverting my own patch in the kernel and replacing it with
>> this, and unfortunately the issue
>> still reproduces here. In Hades 2, a 40FPS limit is locking to 37FPS
>> erroneously.
>
> Interesting... Maybe try reverting fba211b078d6 completely as well.
No change, still locks to 37FPS.
>
> If that doesn't help, could you try isolating FPO by force disabling it
> (without applying this fix, of course)?
> Set `disable_fpo_optimizations = true` in both dcn32_resource.c and
> dcn321_resource.c
Added this change in addition to reverting fba211b078d6, and it now locks to
40FPS rather than 37FPS.
>
> - Leo
>
>>
>> Matt
>>
>>>
>>> Thanks,
>>> Leo
>>>>
>>>> Tracing this led to allow_freesync remaining true for a VRR-capable
>>>> sink even when the FreeSync state was inactive. That allowed FPO to
>>>> stretch vblank around UCLK switches. The PCON whitelist change exposed
>>>> this on our setup by making the sink eligible for that path.
>>>>
>>>> The intent is to keep the frame period fixed when userspace has
>>>> disabled VRR, while retaining FPO eligibility when variable refresh is
>>>> actually requested. With the patch, the original setup holds the
>>>> requested 40fps again. I also tested VRR toggling on a Legion Go 2's
>>>> internal eDP OLED panel and did not observe a regression.
>>>>
>>>> Thanks,
>>>> Matt
>>>
>>
>
